Isn't it illegal what some rappers are doing?

Jason Derulo using (Whatcha say) Flo rida using (You spin me right round, Blue Da Ba Dee) Rihanna (Mia hi) and they don't even say that they're part of the song like with Kanye West and Daft Punk (Harder, Better, Faster, Stronger). I mean, isn't that copy right infringment or something? Plagerism? I mean...I'm tired of seeing that youtube deletes videos that use other songs that belong to people, but there are rappers doing it like crazy. And it's only the rap songs I've heard like this. I haven't heard no rock song that sounds like it's using a verse from Crush 40 (Sonic the Hedgehog) or anything like that.